International Publication No. 2007/069606 describes one example of a semiconductor package. In the semiconductor package, electronic components are arranged between upper and lower substrates, and the surrounding of the electronic components is filled with an encapsulating resin. In such a semiconductor package, the upper substrate is fixed to the lower substrate with spacers arranged in between to maintain the distance between the upper and lower substrates. Under this situation, the encapsulating resin is filled between the upper and lower substrates.
A copper core solder ball may be used as the spacer. The copper core solder ball has a copper core ball and solder, which encompasses the copper core ball. The solder functions as a bonding material, and the copper core ball functions as a spacer. Solder reflow is performed under a situation in which copper core solder balls are arranged between connection pads of the upper substrate and connection pads of the lower substrate. This solder-bonds the connection pads of the upper substrate and the connection pads of the lower substrate. When the solder melts, the copper core balls are held between the connection pads of the upper substrate and the connection pads of the lower substrate and thereby function as spacers. Accordingly, the size of the copper core balls sets the distance between the upper substrate and the lower substrate, and keeps the distance constant.